JP-9-14090A and JP-2002-310030A show a fuel injection valve having an electromagnetic solenoid which magnetically attracts a movable core connected to a valve needle and adapted to cooperate with the valve needle, thereby driving the valve needle directly. The valve needle is adapted to sit on and leave a valve seat. The fuel injection valve of this type is provided with an elastic member such as a spring for urging the valve needle toward the valve seat. The movable core is provided at an end of the valve needle on the side opposite to the valve seat, and a valve member comprising the valve needle and the core is exposed into fuel in the whole area of its end portion opposite to a nozzle hole. More particularly, for example as shown in FIG. 9, fuel of which pressure has been increased to a predetermined pressure is conducted to a fuel inlet formed in a fuel introducing portion 948 of a fuel injection valve 902 on the side opposite to a fuel injection valve 902, then passes through the interior of the fuel injection valve 902 and reaches a nozzle hole 921. In the fuel injection valve 902 thus allowing the fuel to pass therethrough, a whole surface 951a of an upper end portion 951 of a movable core 950 is exposed into the fuel. The upper end portion corresponds to the whole area of the end portion opposite to the nozzle hole. The movable core 950 is connected to a needle 930 and adapted to cooperate with the needle.
When the fuel injection valve closes, the needle is made to sit on the valve seat with the urging force of the elastic member to keep the valve closed. With the valve closed, not only the urging force of the elastic member but also the pressure of the fuel introduced into the fuel injection valve is applied in the valve closing direction.
The direct injection type engine tends to be produced from the standpoint of improving fuel economy and output. However, in case of injecting fuel directly into a combustion chamber from a fuel injection valve, the needle is urged with a large force in the valve closing direction because of a high fuel pressure for direct injection. Moreover, under an inter-cylinder combustion pressure, it is necessary to increase the urging force of the elastic member and urge the needle strongly toward the valve seat lest the needle should be opened with the combustion pressure even when the fuel pressure is low at the time of start-up for example.
Thus, the solenoid requires energy large enough to overcome the urging force induced by fuel and the urging force induced by the elastic member, as a driving force necessary for opening the valve.